Nail-Patella Syndrome
Nail-Patella syndrome (NPS) is a rare genetic disorder that
causes abnormalities of bone, joints, fingernails and kidneys. NPS is commonly
characterized by absent or under-developed kneecaps and thumbnails. It is estimated to
occur in one in 50,000 newborns.
Information about Nail-Patella Syndrome
Nail-patella syndrome (NPS) is a rare genetic disorder that is usually apparent at
birth or during early childhood. Although the symptoms and physical characteristics
associated with NPS may vary, characteristic abnormalities tend to include improper
development (dysplasia) of the fingernails and toenails; absence (aplasia) and/or
underdevelopment (hypoplasia) of the knee caps (patellae); underdevelopment of certain
bones and/or webbing of skin at the bend of the elbow(s); and/or abnormal projections of
bone from the upper (superior) portion of both sides of the hipbone (bilateral iliac
horns).
In addition, some individuals within certain families (kindreds) may have abnormally
increased fluid pressure of the eyes (glaucoma). The condition results due to progressive
blockage of the outflow of fluid (aqueous humor) from the front chamber of the eyes
(open-angle glaucoma). Without appropriate treatment, the gradual increase in fluid
pressure may cause increased narrowing of visual fields and eventual blindness. Other eye
(ocular) abnormalities may also be associated with NPS. For example, in some affected
individuals, the inner margin (pupillary margin) of the colored portion of the eyes
(irides) may appear abnormally dark (hyperpigmentation) and "cloverleaf shaped"
(Lester iris).
Approximately 30 to 40 percent of individuals with NPS may also develop abnormalities in
kidney function (nephropathy) that may be apparent during childhood or later in life.
Nail-patella Syndrome is inherited as an autosomal dominant trait.
Causes of Nail-Patella Syndrome
Nail-patella syndrome is a rare genetic disease. The genetic mutation is an autosomal
dominant mutation. This means that possession of only one copy of the defective gene is
enough to cause disease. The defect has been mapped to chromosome 9 and may be related to
the gene that codes for type 5 collagen. Some patients with this disease show no symptoms
and are discovered to have the disease only when genetic studies trace family histories.
The fingernails of these patients are usually poorly developed or missing. The index
fingers and thumb are most commonly affected by this disease. Fingernails that are present
may be small and concave and have pitting, ridges, splits, and discoloration. Effects are
rarely seen on the toes. Either or both kneecaps may be missing. Abnormally formed
kneecaps can take a variety of shapes. Since the kneecap stabilizes the knee, patients may
have difficulty walking. The iliac crest of the hip bone usually has a pronounced flaring
called iliac horns. Kidney disease may be present. Biopsy shows lesions that resemble
those of inflammation of the clusters of capillaries in the kidneys (glomerulonephritis),
but without any infection present. Kidney failure occurs in about 30% of nail-patella
patients who have kidney involvement. Most patients have excrete protein and blood cells
in their urine (chronic, benign proteinuria and hematuria.)
Symptoms of Nail-Patella Syndrome
The phenotype is characterized by multiple osseous abnormalities, primarily affecting
the elbows and knees and nail dysplasia. About 50% of patients have clinically evident
nephropathy. The disease usually manifests clinically as asymptomatic hematuria and
proteinuria, occasionally in the nephrotic range, but it may be silent. (Harrison's
Principles of Internal Medicine-15th Edition-McGraw-Hill)
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